This invention relates to a process whereby oil field waste brine is utilized to develop and maintain a salt gradient solar pond which in turn provides thermal energy for doing work, including improved separation of oil/brine emulsions into waste bring, crude oil, and natural gas. A salt gradient solar pond (SGSP) is a simple, low-cost device for collecting and storing solar energy. It consists of water whose salt concentration, and therefore density, increases with depth. The deepest zone, i.e., storage area, is heated by incoming solar radiation and, due to its high density, remains near the pond bottom. The upper pond layers act as insulation for the hot brine in the storage layer.
The solar pond has been described as the simplest technique for direct thermal conversion of solar energy. It is simultaneously a collector of solar radiation and a large body of thermal storage. Because of its massive thermal storage and relatively low heat losses, the pond converts an intermittent energy source into a reliable and continuous source of thermal energy.
In a normal body of water a portion of the solar radiant energy penetrates into the sub-layers. As the radiant energy passes through successive layers, it is gradually absorbed and causes the water to warm. The warming decreases the density and the water rises, carrying with it the absorbed solar energy. At the surface, the energy is lost to the atmosphere by radiation, convection, and through evaporation. Thus, the body of water remains cool.
In a salt gradient solar pond, density is made to increase with depth. This condition is achieved with a high salt concentration at the bottom and a low concentration at the surface. With a sufficiently high saline concentration, lower zone waters can absorb solar energy and yet remain denser than the waters immediately above. Bottom-to-surface convection currents are eliminated; therefore, the lower zone waters remain in place and continue to absorb solar energy. Temperatures approaching 100.degree. C. (212.degree. F.) have been observed at the bottom zone of working solar ponds.
Existing crude oil production processes utilize a device known as a "heater treater" to separate crude oil from naturally occurring brines. An emulsion of crude oil/brine, and natural gas flows from production wells into a gathering line and then into a gas-fired heater treater. At the heater treater the emulsion is heated to a desired operating temperature of approximately 140.degree. F. in order to lower the constituent viscosities, and increase differences in specific gravity of brine and oil, thus allowing faster settling of the brine. Consequently, there always exists three distinct commodities within the heater treater, i.e., natural gas, crude oil, and brine. The natural gas produced with the crude oil exits the top of the heater treater. A portion of the natural gas is diverted for consumption as the fuel in the heater treater while most is piped to a compressor. Then, the gas is reinjected into the geologic formation to assist in future oil recovery; it can be recovered for eventual sale whenever economic factors warrant.
The crude oil exits from the heater treater at a level lower than that for the natural gas. It flows into stock tanks to await eventual sale. At this point the crude oil, which may contain as much as 30% brine by weight when produced, normally contains less than 1%.
The brine is the densest commodity produced, so it occupies the lowest portion of the heater treater. From there it is transferred to a storage point, and is periodically collected by a commercial brine disposal vacuum truck. Disposal costs can be considerable to the oil producer. This brine is also regarded as a fresh ground water hazard, and its disposal is closely regulated. The ultimate depository of the brine is usually a carefully chosen well, although a lined pit is an acceptable alternative.